Despite the development of regional trauma centers, improved emergency transport systems to reduce the total time in shock, and aggressive resuscitation, trauma patient mortality and morbidity remains high. Traumatic injury is the leading cause of death in subjects <44 years of age, resulting in over 150,000 deaths annually. Severe hypovolemia due to hemorrhage is a major factor in nearly half of those deaths. Furthermore, patients who survived the initial injury are at a high risk of developing subsequent multiple organ dysfunction syndrome and sepsis with a significant rate of late mortality in the ICU. More effective patient monitoring technology would identify patients at risk to develop organ failure and guide appropriate therapy.
Current monitoring required to assess hemodynamic functionality is often invasive and is limited to high acuity settings. Non-invasive monitoring conducive to lower acuity settings, (i.e., areas of care where invasive and cumbersome monitoring techniques cannot be practically implemented) currently provides static unidimensional isolated information of questionable utility. Recent advances in our understanding of the dynamic nature of circulatory control have introduced novel hemodynamic monitoring approaches that are continuous, noninvasive and metabolic in their orientation. When these monitoring strategies are used as physiology-based feedback to guide caregiver-directed protocolized therapy, they can lead to a new and robust approach to the resuscitation of trauma patients.
This technology can potentially be exported beyond the acute care centers to many areas where less robust conditions for monitoring prevail and smaller form factors become available. This includes ambulance and life flight air transport in the civilian sector and aeromedical evacuation and critical care air transport in the military sector. The ability to provide continuous, autonomous, and quantitative hemodynamic monitoring is also conducive to telemedicine applications and appropriate for highly scalable mass causality care response.
Severe shock associated with trauma is characterized by a decreased effectiveness of circulatory blood flow to meet the metabolic demands of the body. Shock is the result of a vast array of processes with different time courses, degrees of cardiovascular compensation, monitoring needs, pathophysiologies, treatments, and outcomes. However, in all cases, prolonged and unrecognized impaired tissue perfusion will cause organ injury, increased morbidity, and death. Circulatory shock may occur from a variety of reasons, but has as its hallmark, inadequate tissue perfusion, such that ischemic dysfunction and organ injury inevitably develop. If tissue hypoperfusion is not reversed by intravascular fluid resuscitation and/or pharmacologic support aimed at restoring normal cardiac performance and vasomotor tone, organ failure and death occur. However, only half of the patients with cardiovascular insufficiency increase their cardiac output in response to volume loading. Thus, it is important to identify which patients are preload-responsive (i.e. they will increase their cardiac output in response to fluid resuscitation) because giving fluid resuscitation to a patient who is not preload-responsive will not improve their circulatory status and delay effective treatment, when delaying treatment results in organ injury and intravascular volume overload can occur in such patients which induce acute right ventricular failure (acute cor pulmonale) and pulmonary edema, both of which can compromise normal homeostatic mechanisms and induce worsening circulatory shock and death.
Thus, the prior art has at least three major deficiencies. First, the devices available to monitor a patient's systemic stability are quite insensitive. Second, the mechanisms for monitoring such patients requires that patients are either mechanically ventilated or are in an environment in which crude maneuvers may be implemented to perturb the cardiovascular system, such as by raising or abdominal compressions. Finally, the output generated by currently available devices requires competent care providers to interpret the output and to decide appropriate actions or treatment protocols. Thus, there is a need for a device that can use the insensitive signals and transform them into something meaningfully related to the subject's systemic state. There is also a need for a method that can be implemented in a spontaneously breathing subject and/or avoids the inconvenience of physical maneuvers to perturb the cardiovascular system. Finally, there is a need for a device that can be used by a lesser competent care provider, such as emergency response personnel, so that critically ill patients can receive effective treatment quickly.